Conventional air-conditioning systems cool an input air stream by heat exchange with a coil carrying refrigerant material cooled in a cycle of evaporation, compression, heat exchange, and condensation. Such systems are generally costly, of large size, and require large amounts of energy to operate. For vehicle air conditioning systems particularly, the conventional compressor presents a heavy demand on the vehicle's power output. The high power requirement results in lowered vehicle power, reduced miles-per-gallon performance, engine overheating and radiator boilovers under extreme conditions.
Some alternative air cooling systems have used the physical adsorption of water or water vapor from air by dry or liquid adsorbent materials, followed by rehumidification, to produce a cooled air output. These systems make use of the release of heat through the physical bonding of water molecules to adsorbent materials, typically brines, glycols, salt hydrates, alumina, zeolites, and other hygroscopic (water-seeking) materials. One form of liquid adsorption system is described, for example, in Robison U.S. Pat. No. 4,287,721, or in Griffiths U.S. Pat. No. 4,164,125. For cooling, the hot, humid incoming air is adiabatically or (in some systems) isothermally dehumidified through the adsorbent, with the heat of adsorption and some sensible heat being discharged from the system. The dehumidified air is then typically evaporatively cooled through rehumidification with water.
However, the known systems are essentially one-way in operation and require a separate and large volume regenerator system to periodically reconcentrate the diluted adsorbent material, typically through contact with solar heat or some other form of cyclical or daily heat input. These liquid systems also have other disadvantages in terms of: the limited range of operating temperatures or pressures; a relatively limited stored energy capacity through physical adsorption in the range of about 1000 calories per mole; and the required pumping of large volumes of liquid adsorbent into contact with the air stream to be conditioned and during regeneration. These prior systems are particularly unsuited for vehicle air cooling, where compactness and short cycling times are required.
Some types of absorption air conditioners have been tried for automotive use, but they have been found to possess many disadvantages. If they are designed to work using the engine hot water as heat source and the radiator as heat sink, their size becomes too large to be practical. If designed to use the heat of exhaust gases, the size of the system is large, and it does not provide enough heat input during slow moving traffic conditions. Such systems also use liquid absorbents which have a delicate equilibrium sensitive to vibration and acceleration.
By employing chemical compounds having high heat of chemical reaction capacities, as described for example in U.S. Pat. No. 3,075,361 or in the work of Argonne National Laboratory using alkaline or metal hydrides as the heat transfer media, energy potentials of the order of about 10,000 calories per mole or more have been obtained. However, these materials have a high cost and are not considered economically attractive for commercial uses. They also require high temperature heat to regenerate the absorbent material.
It is therefore a principal object of this invention to provide an improved chemisorption apparatus for heating or cooling that has a high heat transfer capacity and yet is inexpensive and simple in design and operation. It is further a specific objective herein to provide a compact and economical vehicle air conditioning system that presents a low demand on the vehicle's power output and uses the vehicle's waste heat as its primary energy source.